This invention relates to a torque control apparatus which is generally applicable to any one of various rotary machines, for example, a compressor in which a load element is driven by a motor, and more particularly to a torque control apparatus suitable for application to a rotary machine in which load torque varies periodically.
JP-A-No. 60-60286 published on Apr. 6, 1985 (corresponding to U.S. Pat. No. 4,604,036 issued, on Aug. 5, 1986) discloses a torque control apparatus in which, in order to minimize the difference (a difference torque) between a load torque of a compressor of a refrigerator and an output torque of a motor driving the compressor through a main shaft, an attempt is made so as to cause the motor to produce an output torque having a pattern which varies in synchronism with variation of the load torque depending on the angular position in one revolution.
In the disclosed apparatus, however, the waveform representing a variation of the load torque is obtained on the basis of a signal, such as pressure variation in a compressor, derived from a machine effecting the refrigeration cycle. Accordingly, the waveform change thus obtained is delayed relative t the actually occurring change in the load torque waveform, and the resultant control of the output torque of the motor cannot completely eliminate vibration of the compressor housing and its supporting system in the direction of rotation of the main shaft.